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January 24 & 25 the annual Digital Cinema Symposium was held hosted by D3Dcinema.
The symposium is an event for showcasing the leading digital cinema technologies for museums and attractions.

I saw some short reports afterwards mostly referring to the general good quality of the 4K content and the RED reel footage used in some of the demo's, but not so much about the 4K digital vs. IMAX 15/70mm.

Recently I found a more detailed report by Howard Hall at the Digital Cinema Society web site.
As we have had several threads discussing 4K digital vs. Imax.

I quote the whole report here so it is easy to find for future references and doesn't disappear into some archive at DCS.

The following observations on 2K, 4K, and 3D Large Screen Digital Projection are a DCS member content contribution from Howard Hall, the noted Underwater Filmmaker/Cinematographer/Photographer and Author after attending last month’s Galveston Digital Symposium:

On January 24 I joined 127 other Giant Screen professionals at the Moody Gardens Theater to see the debut of the Barco 4K 3D projector system and to view a split screen 4K projection versus IMAX 70mm projection comparison. The Moody Gardens giant screen is 72 feet by 53 feet.

During the two-day event we saw only digital projections (aside from the 4K versus 70mm “shootout”). Most of the films were projected in 2K on the Barco 4K capable projectors. The 2K projections were shown via both single and two projector systems demonstrating a variety of glasses including Dolby, active, circular polarized, and linear polarized glasses.

I learned little from the 2K projections other than the differences in glasses technologies. I was very surprised at how effective the Dolby notched filter anaglyph glasses were. These totally occluded the opposite eye allowing no ghosting. This combined with the ability to work with any screen surface made this a compelling choice. Glasses cost about $10. The available Dolby glasses are too small for giant screen viewing however. I am sure there is some color shift present when using the Dolby system, but if so I didn’t notice it.

The linear polarized glasses produced the most ghosting which was made more significant when tilting one’s head to the side. Circular polarized glasses were better. Both had more ghosting than Dolby. The active shutter glasses may have produced the best image, but were darker than the others. Active glasses have other well-known maintenance disadvantages when used in commercial venues. Both Dolby and circular polarized systems can be used on single projector system via a spinning filter wheel. They can be used on duel projector systems via discrete filters.

The 2K projections produced a significantly degraded giant screen experience. Although there was no direct comparison with 70mm, the difference was obvious and visceral.

The 4K projections were another story. We saw a RED Cinema demo reel that was stunning. My impression was that it looked as sharp as any 70mm projection. The image “seemed” to fill the giant screen and had excellent contrast, resolution, and saturation. It wasn't until the lights came back up that I noticed that the top of the screen had not been used.

The “shootout” between 70mm and 4K was most interesting. We saw two clips projected via split screen then we saw the clips projected alternately. The first 70mm clip from “Pulse” was printed in the traditional way via negative, interpositive, and duplicate negative. The second 70mm clip (from Wild Ocean) was made in the more modern way via 11K scan from negative, then a 4K down-conversion, then film-out to 70mm. The digital projections were made via 11K scan and then 4K down-conversion. The 4K file of Wild Ocean was the file used for the film-out.

Just comparing the two 70mm clips was enlightening. The “Pulse” clip was significantly better than the film-out version of Wild Ocean. Scanning and film-out of Wild Ocean had been necessary because so many different formats in addition to 70mm were used in original image capture (we saw only 70mm original capture examples). Andrew Orin from FotoKem who made the film prints, estimated that even the “Pulse” clip had degraded to between 5.5 and 6K via the printing process (assuming original camera negative is about 11K).

In my opinion the split screen comparison showed that 4K projection is equal to or better than 70mm projection in all respects save one. The digital images appeared as sharp or sharper, they appeared to have more contrast in addition to equal or better resolution, and the color saturation and fidelity was equal or better. These differences were minor and debatable when the two “Pulse” clips were compared. The differences were dramatic when Wild Ocean was up.

The only remaining advantage to the 70mm projection was that the 4K projection was 16x9 and did not fill the vertical axis of the screen. That the bottom of the 4K screen image was missing was of no consequence to me since audience heads occlude the 70mm image at the bottom and to me this may be viewed as a distraction. The top of the screen is another story however. Some of the experiential effect is lost with the 4K projection though I confess I did not miss it much. This was the only disadvantage to 4K digital capture and projection that I could see and was but one point when scored against the myriad disadvantages, both financial and logistical, of shooting and projection in 70mm.

When the audience was asked which image they liked best, the overwhelming response was that they preferred the digital projection. As an IMAX 70mm veteran, I found that quite astounding.

I recognize that the 16x9 aspect ratio will be much more problematic for giant screen dome theaters. Also Moody Gardens has a modestly sized IMAX screen. Digital light levels may be problematic on the very largest IMAX giant screens some of which are up to 100 feet wide.